Justice is a by-product of law. Law is meant to be a deterrent against things undesirable in society, and it exists to provide punishment to those guilty of a crime. She was found guilty of the crime - therefore, she bears the punishment.
Besides, justice is subjective. Your notion of justice will probably disagree with someone else's, and you'd both be right insofar that you both express opinions that correspond with your respective core values.
Law isn't mean to be just. Law is meant to be objective. The court, therefore, is a place where the super-ego notion of the higher duty of law is getting reconciled with the pain of damaged outlook that is the desire for justice.